Physical layer aware video encoding for mobile tv applications

ABSTRACT

A system and method of transmitting video in a time division multiplexing (TDM) system, wherein the method comprises identifying a video reference frame from a series of video frames; encoding a difference between the video reference frame and a video non-reference frame; placing the video reference frame at a beginning of a data burst; transmitting the series of video frames and the data burst from a transmitter to a mobile TV receiver; and the mobile TV receiver immediately locating the video reference frame upon receipt of the data burst. The method may further comprise the mobile TV receiver decoding the series of video frames. Additionally, the placing process results in a substantially non-existent channel switching delay in the mobile TV receiver. Moreover, the method may further comprise placing exactly one video reference frame at the beginning of the data burst. Preferably, the TDM system comprises a mobile TV system.

BACKGROUND

1. Technical Field

The embodiments herein generally relate to wireless technologies, and,more particularly, to mobile television (TV) technologies.

2. Description of the Related Art

In mobile TV Digital Video Broadcasting over Handheld (DVB-H) systemssuch as DVB-H (ETSI EN 301 192), one radio frequency (RF) channel isshared among many TV channels (TV programs). These TV channels aremultiplexed either in the time domain or in the frequency domain. Whenthe TV channels are multiplexed in the time domain, each channel isgiven full access to the entire RF channel bandwidth for a short periodof time (burst duration). After that burst is transmitted, bursts forother channels occupy the RF channel and so on. This multiplexingprocess is called time division multiplexing (TDM). FIG. 1 illustratesan example of time division multiplexing of 15 TV channels on one RFchannel. The TV channels are labeled 1, 2, 3, . . . , 15. In FIG. 1, itis shown that each TV channel occupies the entire RF channel for 1/15 ofthe time. A receiver which is watching only one channel (for example,channel 2) needs only to be active (ON) during the periods of channel 2bursts. In order to conserve battery consumption, such a receiver willtypically shut off its circuits when channel 2 bursts are not occupyingthe RF channel. The receiver thus enters into a SLEEP mode. This showsthat the TDM of channels can help reduce power consumption of a receiverwatching a single channel.

On the other hand, this causes a problem when the user wants to switchto watch another TV channel on the same RF channel. One example is shownin FIG. 1, if the user wishes to switch to Channel 3 (denoted by ChannelUP in FIG. 1). The worst case occurs when the user issues a command toswitch to Channel 3 right after the burst of Channel 3 ends. In thiscase, the receiver has to wait until the next burst that belongs toChannel 3 appears on the RF channel. This causes the user to wait for agiven period of time denoted as the channel switching delay. Such adelay could be as long as 5 to 7 seconds in DVB-H systems. Such channelswitching delay could be rather annoying to the user. This delay isknown as the delay in the physical layer or the PHY delay.

In addition to the PHY delay, there is an additional delay in thephysical layer that arises from the nature of the video encodingprocess. Digital video encoding techniques normally treat a video signalas a stream of still pictures (video frames). The encoding processstarts by encoding one frame independently of other frames. Such a frameis called the reference frame (I-frame). For the following frames, thevideo encoder finds the difference between each frame and the referenceframe. The video encoder encodes only this difference in order to reducethe bit rate of the encoded video stream. In practice the size of areference frame is significantly larger than a regular frame (P-frame).Video encoders transmit I-frames at a low rate that could be as low asone reference frame per second.

At the receiver, video frames are generally received in order. When theuser switches to a given channel, the receiver waits for the firstavailable reference frame to start decoding the video. The video decoderneglects all P-frames until it finds the first I-frame. After receivingthe first I-frame, the video decoder can now decode all frames and theuser can then start watching video. The amount of time between receivinga given channel and finding the first reference frame is a delay in theoverall channel switching operation. The worst case delay depends on howoften reference frames are transmitted. For example, if reference framesare transmitted once per second, then the worst case time delay is onesecond. In order to reduce such a delay, the transmitter has to transmitreference frames at a high rate, which could reduce the overall channelcapacity as reference frames are significantly larger than normalframes. Accordingly, there remains a need for a new video encodingtechnique for mobile TV applications.

SUMMARY

In view of the foregoing, an embodiment provides a method oftransmitting video in a TDM system, wherein the method comprisesidentifying a video reference frame from a series of video frames;encoding a difference between the video reference frame and a videonon-reference frame; placing the video reference frame at a beginning ofa data burst; transmitting the series of video frames and the data burstfrom a transmitter to a mobile TV receiver; and the mobile TV receiverimmediately locating the video reference frame upon receipt of the databurst. The method may further comprise the mobile TV receiver decodingthe series of video frames. Additionally, the placing process results ina substantially non-existent channel switching delay in the mobile TVreceiver. Moreover, the method may further comprise placing exactly onevideo reference frame at the beginning of the data burst. Preferably,the TDM system comprises a mobile TV system.

Another embodiment provides a system for transmitting video in a TDMenvironment, wherein the system comprises a TV channel transmittercomprising a video encoder adapted to identify a video reference framefrom a series of video frames and encode a difference between the videoreference frame and a video non-reference frame; and a firstencapsulator adapted to place the video reference frame at a beginningof a data burst, wherein the TV channel transmitter is adapted totransmit the series of video frames and the data burst. The systemfurther comprises a mobile TV receiver in communication with the TVchannel transmitter, wherein the mobile TV receiver comprises a videodecoder adapted to receive the transmitted series of video frames andthe data burst; and a second encapsulator adapted to immediately locatethe video reference frame upon receipt of the data burst.

Preferably, the video decoder is adapted to decode the series of videoframes. Also, placement of the video reference frame at the beginning ofthe data burst preferably results in a substantially non-existentchannel switching delay in the mobile TV receiver. Furthermore, thefirst encapsulator may be adapted to place exactly one video referenceframe at the beginning of the data burst. Moreover, the firstencapsulator may be adapted to feed back to the video encoder a timingof the beginning of the data burst. Additionally, the video encoder maybe adapted to identify a duration of the data burst and a duty cycle ofthe first encapsulator, and wherein the video encoder is adapted togenerate the video reference frame at a same duty cycle as that beinggenerated by the first encapsulator. Preferably, the second encapsulatoris adapted to locate the video reference frame coming from the videodecoder, and wherein the second encapsulator is adapted to link thebeginning of the data burst to a location of the video reference frame.Also, the TDM environment preferably comprises a mobile TV environment.

Another embodiment provides a system of transmitting video in a TDMsystem, wherein the system comprises means for identifying a videoreference frame from a series of video frames; means for encoding adifference between the video reference frame and a video non-referenceframe; means for placing the video reference frame at a beginning of adata burst; means for transmitting the series of video frames and thedata burst from a transmitter to a mobile TV receiver; and means for themobile TV receiver immediately locating the video reference frame uponreceipt of the data burst. The mobile TV receiver may further comprisemeans for decoding the series of video frames. Additionally, the placingof the video reference frame at the beginning of the data burstpreferably results in a substantially non-existent channel switchingdelay in the mobile TV receiver. Moreover, the system may furthercomprise means for placing exactly one video reference frame at thebeginning of the data burst. Also, the TDM system may comprise a mobileTV system.

These and other aspects of the embodiments herein will be betterappreciated and understood when considered in conjunction with thefollowing description and the accompanying drawings. It should beunderstood, however, that the following descriptions, while indicatingpreferred embodiments and numerous specific details thereof, are givenby way of illustration and not of limitation. Many changes andmodifications may be made within the scope of the embodiments hereinwithout departing from the spirit thereof, and the embodiments hereininclude all such modifications.

BRIEF DESCRIPTION OF THE DRAWINGS

The embodiments herein will be better understood from the followingdetailed description with reference to the drawings, in which:

FIG. 1 is a schematic diagram illustrating a burst sequence;

FIG. 2 is a schematic diagram illustrating a system according to anembodiment herein; and

FIG. 3 is a flow diagram illustrating a preferred method according to anembodiment herein.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

The embodiments herein and the various features and advantageous detailsthereof are explained more fully with reference to the non-limitingembodiments that are illustrated in the accompanying drawings anddetailed in the following description. Descriptions of well-knowncomponents and processing techniques are omitted so as to notunnecessarily obscure the embodiments herein. The examples used hereinare intended merely to facilitate an understanding of ways in which theembodiments herein may be practiced and to further enable those of skillin the art to practice the embodiments herein. Accordingly, the examplesshould not be construed as limiting the scope of the embodiments herein.

As mentioned, there remains a need for a new video encoding techniquefor mobile TV applications. The embodiments herein achieve this byproviding techniques for reducing the channel switching delay in TDMmobile TV systems such as DVB-H and MediaFlo™ that arises from theplacement of reference frames.

Referring now to the drawings, and more particularly to FIGS. 2 and 3,where similar reference characters denote corresponding featuresconsistently throughout the figures, there are shown preferredembodiments. In order to reduce the channel switching delay due toplacement of reference frames, one or many of the following embodimentscould be used, as indicated in FIG. 2, which illustrates a communicationsystem 100 comprising a receiver 101 and a transmitter 102, wherein thetransmitter 102 places a reference frame 103 at the start of each databurst 111.

The transmitter 102 makes sure that a reference frame 103 exists at thebeginning of each data burst 111. The transmitter 102 is adapted toplace reference frames 103 at arbitrary time instants. The transmitter102 has access to the un-coded video frames. A reference frame 103corresponds only to one video frame, while a non-reference frame 109contains the difference between the current video frame and the previousvideo frames. Thus, placing a reference frame 103 at a given instance intime simply means that the transmitter 102 sends the actual video framecorresponding to this specific instance and not the difference. Thisway, when the receiver 101 starts receiving frames 104 at the start ofthe data burst 111, the receiver 101 finds a reference frame 103immediately. This reduces the delay due to placement of reference frames103 to zero if the receiver 101 wakes up (from a sleep mode ofoperation) before the data burst 111.

Alternatively, the transmitter 102 places only one reference frame 103in each data burst 111, which is at the start of the data burst 111.This significantly reduces the amount of data required for sending theencoded video. For example, if a data burst 111 is transmitted everyfive seconds and the reference frame rate is one reference frame/second,then each data burst would normally include five reference frames 103.If one now sends only one reference frame 103 in each data burst 111,one may save four reference frames 103 per data burst 111 and thusreduce the overall bit rate needed. This still guarantees that thereceiver 101 will correctly decode the video in the data burst 111 if itwakes up (from a sleep mode of operation) before the data burst 111 andthus gets the only reference frame 103 in the data burst 111.

If the receiver 101 wakes up in the middle of the data burst 111,thereby missing the only reference frame 103, then the receiver 101waits for the next data burst 111 to get a reference frame 103. However,since the duty cycle of the data bursts 111 is usually very low, theprobability of the receiver 101 waking up (from a sleep mode ofoperation) during any given data burst 111 is very low.

Preferably, the encapsulator 105, which is responsible for the databurst timing control, feeds back to the video encoder 106, which isresponsible for inserting reference frames 103 the timing of the databurst start. The video encoder 106 ensures that a reference frame 103 isinserted at the start of the data burst 111. If the video encoder 106knows the time instant of a reference frame 103 it simply sends theactual frame at this instant and not the frame difference.

The video encoder 106 knows the burst duration and duty cycle from theencapsulator 105 and generates reference frames 103 at the same dutycycle. Moreover, the encapsulator 108 locates the reference frames 103coming from the video decoder 107 and adapts the start of the data burst111 to the location of the reference frames 103. The encapsulator 108 isadapted to place the start of data bursts 111 at any time instance. Oncethe encapsulator 108 locates the time instance of a reference frame 103(a reference frame 103 has a header that could be detected), it placesthe data burst start at this time instance.

FIG. 3, with reference to FIGS. 1 and 2, is a flow diagram illustratinga method of transmitting video in a TDM system 100, wherein the methodcomprises identifying (301) a video reference frame 103 from a series ofvideo frames 104; encoding (303) a difference between the videoreference frame 103 and a video non-reference frame 109; placing (305)the video reference frame 103 at a beginning of a data burst 111;transmitting (307) the series of video frames 104 and the data burst 111from a transmitter 102 to a mobile TV receiver 101; and the mobile TVreceiver 101 immediately locating (309) the video reference frame 103upon receipt of the data burst 111. The method may further comprise themobile TV receiver 101 decoding the series of video frames 104.Additionally, the placing process (305) results in a substantiallynon-existent channel switching delay in the mobile TV receiver 101.Moreover, the method may further comprise placing exactly one videoreference frame 103 at the beginning of the data burst 111. Preferably,the TDM system 100 comprises a mobile TV system.

The techniques provided by the embodiments herein may be implemented onan integrated circuit (IC) chip or using printable electronictechnologies (not shown). The chip or printable electronic circuitdesign is created in a graphical computer programming language, andstored in a computer storage medium (such as a disk, tape, physical harddrive, or virtual hard drive such as in a storage access network). Ifthe designer does not fabricate chips or printable electronic circuitsor the photolithographic masks used to fabricate chips or printableelectronic circuits, the designer transmits the resulting design byphysical means (e.g., by providing a copy of the storage medium storingthe design) or electronically (e.g., through the Internet) to suchentities, directly or indirectly. The stored design is then convertedinto the appropriate format (e.g., GDSII or CIF) for the fabrication ofphotolithographic masks, which typically include multiple copies of thechip design in question that are to be formed on a wafer or printed on asuitable substrate. The photolithographic masks are utilized to defineareas of the wafer or printable electronic circuits (and/or the layersthereon) to be etched or otherwise processed or printed.

The resulting integrated circuit chips or printable electronic circuitscan be distributed by the fabricator in raw wafer form (that is, as asingle wafer that has multiple unpackaged chips), as a bare die, or in apackaged form or as individual printed circuits or in a sheet or roll ofprinted circuits. In the latter case the chip is mounted in a singlechip package (such as a plastic carrier, with leads that are affixed toa motherboard or other higher level carrier) or in a multichip package(such as a ceramic carrier that has either or both surfaceinterconnections or buried interconnections). In any case the chip mightthen be integrated with other chips, discrete circuit elements, and/orother signal processing devices as part of either (a) an intermediateproduct, such as a mother or daughter-board, or (b) an end product. Theend product can be any product that includes integrated circuit chip orchips and/or printed circuits, ranging from toys and other low-endapplications to advanced computer products having a display, a keyboardor other input device, and a central processor.

The foregoing description of the specific embodiments will so fullyreveal the general nature of the embodiments herein that others can, byapplying current knowledge, readily modify and/or adapt for variousapplications such specific embodiments without departing from thegeneric concept, and, therefore, such adaptations and modificationsshould and are intended to be comprehended within the meaning and rangeof equivalents of the disclosed embodiments. It is to be understood thatthe phraseology or terminology employed herein is for the purpose ofdescription and not of limitation. Therefore, while the embodimentsherein have been described in terms of preferred embodiments, thoseskilled in the art will recognize that the embodiments herein can bepracticed with modification within the spirit and scope of the appendedclaims.

1. A method of transmitting video in a time division multiplexing (TDM)system, said method comprising: identifying a video reference frame froma series of video frames; encoding a difference between said videoreference frame and a video non-reference frame; placing said videoreference frame at a beginning of a data burst; transmitting said seriesof video frames and said data burst from a transmitter to a mobile TVreceiver; and said mobile TV receiver immediately locating said videoreference frame upon receipt of said data burst.
 2. The method of claim1, further comprising said mobile TV receiver decoding said series ofvideo frames.
 3. The method of claim 1, wherein the placing processresults in a substantially non-existent channel switching delay in saidmobile TV receiver.
 4. The method of claim 1, further comprising placingexactly one video reference frame at said beginning of said data burst.5. The method of claim 1, wherein said TDM system comprises a mobile TVsystem.
 6. A system for transmitting video in a time divisionmultiplexing (TDM) environment, said system comprising: a TV channeltransmitter comprising: a video encoder adapted to identify a videoreference frame from a series of video frames and encode a differencebetween said video reference frame and a video non-reference frame; anda first encapsulator adapted to place said video reference frame at abeginning of a data burst, wherein said TV channel transmitter isadapted to transmit said series of video frames and said data burst, amobile TV receiver in communication with said TV channel transmitter,said mobile TV receiver comprising: a video decoder adapted to receivethe transmitted series of video frames and said data burst; and a secondencapsulator adapted to immediately locate said video reference frameupon receipt of said data burst.
 7. The system of claim 6, wherein saidvideo decoder is adapted to decode said series of video frames.
 8. Thesystem of claim 6, wherein placement of said video reference frame atsaid beginning of said data burst results in a substantiallynon-existent channel switching delay in said mobile TV receiver.
 9. Thesystem of claim 6, wherein said first encapsulator is adapted to placeexactly one video reference frame at said beginning of said data burst.10. The system of claim 6, wherein said first encapsulator is adapted tofeed back to said video encoder a timing of said beginning of said databurst.
 11. The system of claim 6, wherein said video encoder is adaptedto identify a duration of said data burst and a duty cycle of said firstencapsulator, and wherein said video encoder is adapted to generate saidvideo reference frame at a same duty cycle as that being generated bysaid first encapsulator.
 12. The system of claim 6, wherein said secondencapsulator is adapted to locate said video reference frame coming fromsaid video decoder, and wherein said second encapsulator is adapted tolink said beginning of said data burst to a location of said videoreference frame.
 13. The system of claims 6, wherein said TDMenvironment comprises a mobile TV environment.
 14. A system oftransmitting video in a time division multiplexing (TDM) system, saidsystem comprising: means for identifying a video reference frame from aseries of video frames; means for encoding a difference between saidvideo reference frame and a video non-reference frame; means for placingsaid video reference frame at a beginning of a data burst; means fortransmitting said series of video frames and said data burst from atransmitter to a mobile TV receiver; and means for said mobile TVreceiver immediately locating said video reference frame upon receipt ofsaid data burst.
 15. The system of claim 14, further comprising saidmobile TV receiver comprising means for decoding said series of videoframes.
 16. The system of claim 14, wherein the placing of said videoreference frame at said beginning of said data burst results in asubstantially non-existent channel switching delay in said mobile TVreceiver.
 17. The system of claim 14, further comprising means forplacing exactly one video reference frame at said beginning of said databurst.
 18. The system of claim 14, wherein said TDM system comprises amobile TV system.